1. Field of the Invention
The present invention relates generally to mechanical vibration reduction and, more particularly, is concerned with an apparatus and method for automatically reducing vibration of a machine having a rotating component, particularly such as a water-cooled pump having a central rotating shaft.
2. Description of the Prior Art
A common problem in all types of rotating machinery is vibration induced by misalignment, unbalance, functional interactions, and dimensional tolerance variations of rotating components of the machinery. The vibrations occur at a number of frequencies. One frequency of particular concern and interest in machinery such as a water circulating pump is the frequency equal to the running speed of the rotating component.
The particular water pump in question has an upright housing fastened at its lower end to a mounting structure and a central drive shaft rotatably mounted vertically in the housing by a pair of upper and lower radial bearings. The central drive shaft is positioned axially in the housing by a thrust bearing Rotor and stator components of an electric motor for driving the pump drive shaft are incorporated in the housing between the locations of the bearings and an impeller is attached to the lower end of the shaft for rotation therewith to draw water in a central bottom suction nozzle and pump water from a side discharge nozzle on the pump housing The pump also incorporates an internal auxiliary system for pumping water internally along the portion of its shaft which is coextensive with the components of the pump motor for water-cooling the motor.
Rotation of the central drive shaft of the pump induces radial vibratory forces on the upright housing through the radial bearings and through the cooling water between the motor rotor and stator components. The presence of the cooling water in that annulus serves to amplify the radial vibratory forces on the housing. Through the impeller interaction with the pumped water, the central drive shaft also induces axial vibratory forces on the housing through the axial thrust bearing. In response to these vibratory forces, the housing vibrates at the frequency of the rotating speed of the drive shaft in several modes of vibration. One mode is a lateral vibration which results in side-to-side rocking movement of the drive shaft and pump housing. Another mode is an axial vibration which results in up-and-down movement of the drive shaft and pump housing. The motions resulting from these vibratory modes are transmitted both to the water being pumped by the pump impeller and to the mounting structure via the lower end of the housing where the pump is rigidly fastened to the mounting structure.
As can be readily realized, these vibrations are a problem and highly undesirable in many applications for a pump of this general construction. Consequently, a need exists for an improved technique for reducing vibration induced in a machine by a rotating component of the machine.